I was looking for a small WSPR beacon for portable use. When reading the blog of Roger, G3XBM, I ran into the WISPY TX beacon. I converted his 20m beacon to a 30m version. Instead of a passive mixer, I used a NE602 chip. The 10.138 MHz crystal was bought at the
German "FUNK" magazine. Using this xtal and some fine-tuning activity you end up in the
WSPR segment of the 30m band.
The NE602 mixer makes use of a Gilbert cell. This cell assures that the original local
oscillator signal is better suppressed than when using a passive mixer circuit.
There is a disadvantage however. Since this is a Double Sideband Transmitter,
an estimated 100 mW RF power is spilled in the unused sideband. There is no such thing
as a free meal. I connected the beacon to an ATU which feeds the G5RV jr antenna in my garden. The LF signal from the PC is fed into the NE602. The oscillator inside the NE602
is not used.
De power supply voltage is 12 Vdc, derived from an ordinary 7812 that did not get hot after one-day uninterrupted use. An IRF mosfet has been installed for future use in the PA (not connected yet). Currently the PA stage consists of only 2 general-use 2N3904 transistors. Isn't that amazing ?
Circuit of the 30m QRPp beacon
Some stations reported my beacon on February 16, 2013; not that bad for
about 100 milliwatts RF.
The beacon connected to an EeePC to generate WSPR signals. In the left upper corner you can see a 2N2219A which I used in the PA as well.